:root {
  --black: #0b0b0a;
  --white: #f6f6f3;
  --muted-on-dark: rgba(246, 246, 243, 0.62);
  --muted-on-light: rgba(11, 11, 10, 0.6);
  --line-on-dark: rgba(246, 246, 243, 0.14);
  --line-on-light: rgba(11, 11, 10, 0.12);
  --font: "Pretendard Variable", Pretendard, -apple-system, BlinkMacSystemFont,
    "Apple SD Gothic Neo", "Malgun Gothic", "Segoe UI", sans-serif;
}

* {
  box-sizing: border-box;
}

html,
body {
  margin: 0;
  padding: 0;
  width: 100%;
  height: 100%;
  overflow: hidden;
  background: var(--black);
  font-family: var(--font);
  -webkit-font-smoothing: antialiased;
}

#deck {
  position: relative;
  width: 100vw;
  height: 100vh;
  overflow: hidden;
}

#track {
  display: flex;
  height: 100%;
  transition: transform 0.65s cubic-bezier(0.65, 0, 0.35, 1);
  will-change: transform;
}

.slide {
  position: relative;
  flex: 0 0 100vw;
  height: 100%;
  display: flex;
  flex-direction: column;
  padding: clamp(2rem, 5vw, 5rem) clamp(2rem, 5vw, 5rem)
    clamp(6.5rem, 9vw, 8rem);
  overflow: hidden;
}

.slide.theme-dark {
  background: var(--black);
  color: var(--white);
}

.slide.theme-light {
  background: var(--white);
  color: var(--black);
}

.slide::before {
  content: "";
  position: absolute;
  inset: 1.1rem;
  border-radius: 32px;
  pointer-events: none;
  border: 1px solid transparent;
}

.slide.theme-dark::before {
  border-color: var(--line-on-dark);
}

.slide.theme-light::before {
  border-color: var(--line-on-light);
}

/* ---------- shared components ---------- */

.pill {
  display: inline-flex;
  align-items: center;
  gap: 0.45em;
  padding: 0.55em 1.15em;
  border-radius: 999px;
  border: 1px solid currentColor;
  font-size: 0.78rem;
  font-weight: 600;
  letter-spacing: 0.04em;
  text-transform: uppercase;
  white-space: nowrap;
}

.icon-circle {
  width: 2.6rem;
  height: 2.6rem;
  border-radius: 50%;
  border: 1px solid currentColor;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.1rem;
  flex: none;
}

.topbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  z-index: 2;
}

.topbar-left,
.topbar-right {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.brand {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  font-weight: 700;
  font-size: 0.95rem;
  letter-spacing: -0.01em;
}

.brand .dot {
  width: 0.5rem;
  height: 0.5rem;
  border-radius: 50%;
  background: currentColor;
}

.footnote {
  position: absolute;
  left: clamp(2rem, 5vw, 5rem);
  bottom: clamp(4.6rem, 6vw, 5.4rem);
  font-size: 0.68rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  z-index: 2;
}

.theme-dark .footnote {
  color: var(--muted-on-dark);
}

.theme-light .footnote {
  color: var(--muted-on-light);
}

.watermark {
  position: absolute;
  right: clamp(0.5rem, 3vw, 3rem);
  bottom: clamp(-3rem, -3vw, -1rem);
  font-size: clamp(9rem, 24vw, 22rem);
  font-weight: 800;
  line-height: 1;
  letter-spacing: -0.04em;
  opacity: 0.05;
  pointer-events: none;
  user-select: none;
  z-index: 1;
}

/* ---------- title slide ---------- */

.slide-title .headline {
  flex: 1;
  display: flex;
  flex-direction: column;
  justify-content: center;
  z-index: 2;
}

.slide-title .eyebrow {
  font-size: 0.85rem;
  font-weight: 700;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--muted-on-light);
  margin-bottom: 1.4rem;
}

.slide-title h1 {
  font-size: clamp(2.3rem, 5.4vw, 4.6rem);
  font-weight: 800;
  line-height: 1.16;
  letter-spacing: -0.02em;
  margin: 0;
}

.slide-title .subtitle {
  margin: 1.6rem 0 0;
  font-size: clamp(1.05rem, 1.7vw, 1.35rem);
  color: var(--muted-on-light);
  max-width: 46ch;
  line-height: 1.55;
}

.infobar {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 1.5rem;
  border-top: 1px solid var(--line-on-light);
  padding-top: 1.6rem;
  z-index: 2;
}

.infobar .item .label {
  font-size: 0.72rem;
  font-weight: 600;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--muted-on-light);
  margin-bottom: 0.5rem;
}

.infobar .item .value {
  font-size: clamp(1rem, 1.6vw, 1.3rem);
  font-weight: 700;
  letter-spacing: -0.01em;
}

/* ---------- student slide ---------- */

.slide-student .student-body {
  flex: 1;
  display: flex;
  flex-direction: column;
  justify-content: center;
  max-width: 62%;
  z-index: 2;
}

.slide-student .index-label {
  font-size: 0.85rem;
  font-weight: 700;
  letter-spacing: 0.1em;
  margin-bottom: 1.6rem;
  opacity: 0.75;
}

.slide-student h2 {
  font-size: clamp(2.8rem, 7vw, 6rem);
  font-weight: 800;
  line-height: 1.02;
  letter-spacing: -0.03em;
  margin: 0;
}

.slide-student .intro {
  margin: 1.6rem 0 0;
  font-size: clamp(1.05rem, 1.7vw, 1.45rem);
  line-height: 1.6;
  max-width: 40ch;
}

.theme-dark .intro {
  color: var(--muted-on-dark);
}

.theme-light .intro {
  color: var(--muted-on-light);
}

.demo-btn {
  margin-top: 2.6rem;
  align-self: flex-start;
  display: inline-flex;
  align-items: center;
  gap: 0.65em;
  padding: 1em 1.9em;
  border-radius: 999px;
  border: none;
  font-family: inherit;
  font-weight: 700;
  font-size: 1rem;
  letter-spacing: -0.01em;
  cursor: pointer;
  transition: transform 0.2s ease, box-shadow 0.2s ease;
}

.theme-light .demo-btn {
  background: var(--black);
  color: var(--white);
}

.theme-dark .demo-btn {
  background: var(--white);
  color: var(--black);
}

.demo-btn:hover {
  transform: translateY(-3px);
}

.theme-light .demo-btn:hover {
  box-shadow: 0 14px 28px rgba(11, 11, 10, 0.22);
}

.theme-dark .demo-btn:hover {
  box-shadow: 0 14px 28px rgba(0, 0, 0, 0.35);
}

.demo-btn .arrow {
  transition: transform 0.2s ease;
}

.demo-btn:hover .arrow {
  transform: translate(2px, -2px);
}

/* ---------- closing slide ---------- */

.slide-closing {
  align-items: center;
  justify-content: center;
  text-align: center;
}

.slide-closing .icon-circle {
  width: 3.4rem;
  height: 3.4rem;
  margin: 0 auto 2rem;
  font-size: 1.3rem;
}

.slide-closing h1 {
  font-size: clamp(3rem, 8vw, 6.5rem);
  font-weight: 800;
  letter-spacing: -0.03em;
  margin: 0;
}

.slide-closing .subtitle {
  margin-top: 1.2rem;
  font-size: clamp(1rem, 1.6vw, 1.3rem);
  color: var(--muted-on-dark);
}

/* ---------- navigation ---------- */

#nav {
  position: fixed;
  left: 50%;
  bottom: 2rem;
  transform: translateX(-50%);
  display: flex;
  align-items: center;
  gap: 1.1rem;
  z-index: 100;
  color: #fff;
  mix-blend-mode: difference;
}

#nav button {
  width: 2.7rem;
  height: 2.7rem;
  border-radius: 50%;
  border: 1px solid currentColor;
  background: transparent;
  color: inherit;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.1rem;
  transition: background 0.2s ease;
}

#nav button:hover:not(:disabled) {
  background: rgba(255, 255, 255, 0.12);
}

#nav button:disabled {
  opacity: 0.3;
  cursor: default;
}

#nav .counter {
  font-variant-numeric: tabular-nums;
  font-size: 0.85rem;
  font-weight: 600;
  letter-spacing: 0.04em;
  min-width: 4.6rem;
  text-align: center;
}

#progressbar {
  position: fixed;
  left: 0;
  bottom: 0;
  height: 3px;
  width: 100%;
  z-index: 100;
  background: rgba(255, 255, 255, 0.16);
  mix-blend-mode: difference;
}

#progressbar .fill {
  height: 100%;
  width: 0%;
  background: #fff;
  transition: width 0.5s ease;
}

@media (max-width: 720px) {
  .slide-student .student-body {
    max-width: 100%;
  }
  .infobar {
    grid-template-columns: 1fr;
    gap: 1rem;
  }
}